Three-dimensional semiconductor memory device

ABSTRACT

A three-dimensional semiconductor memory device includes an electrode structure including gate electrodes and insulating layers, which are alternately stacked on a substrate, a semiconductor pattern extending in a first direction substantially perpendicular to a top surface of the substrate and penetrating the electrode structure, a tunnel insulating layer disposed between the semiconductor pattern and the electrode structure, a blocking insulating layer disposed between the tunnel insulating layer and the electrode structure, and a charge storing layer disposed between the blocking insulating layer and the tunnel insulating layer. The charge storing layer includes a plurality of first charge trap layers having a first energy band gap, and a second charge trap layer having a second energy band gap larger than the first energy band gap. The first charge trap layers are embedded in the second charge trap layer between the gate electrodes and the semiconductor pattern.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to Korean PatentApplication No. 10-2017-0148953, filed on Nov. 9, 2017, the disclosureof which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

Exemplary embodiments of the present inventive concept relate to athree-dimensional semiconductor memory device, and more particularly, toa three-dimensional semiconductor memory device having improvedreliability and increased integration density.

DISCUSSION OF THE RELATED ART

Higher integration of semiconductor devices is an important factor thatcontributes to satisfying consumer demands for superior performance andinexpensive prices relating to products including semiconductor devices.In the case of two-dimensional or planar semiconductor devices, sincetheir integration is primarily determined by the area occupied by a unitmemory cell, integration is greatly influenced by the level of a finepattern forming technology. However, the expensive process equipmentneeded to increase pattern fineness sets a practical limitation onincreasing integration for two-dimensional or planar semiconductordevices. To overcome such a limitation, three-dimensional semiconductormemory devices including three-dimensionally arranged memory cells haverecently been proposed.

SUMMARY

Exemplary embodiments of the inventive concept provide athree-dimensional semiconductor memory device having improvedreliability and increased integration density.

According to exemplary embodiments of the inventive concept, athree-dimensional semiconductor memory device includes an electrodestructure including a plurality of gate electrodes and a plurality ofinsulating layers, which are alternately stacked on a substrate, asemiconductor pattern extending in a first direction substantiallyperpendicular to a top surface of the substrate and penetrating theelectrode structure, a tunnel insulating layer disposed between thesemiconductor pattern and the electrode structure, a blocking insulatinglayer disposed between the tunnel insulating layer and the electrodestructure, and a charge storing layer disposed between the blockinginsulating layer and the tunnel insulating layer. The charge storinglayer includes a plurality of first charge trap layers, each of whichhas a first energy band gap, and a second charge trap layer, which has asecond energy band gap larger than the first energy band gap. The firstcharge trap layers are embedded in the second charge trap layer betweenthe gate electrodes and the semiconductor pattern.

According to exemplary embodiments of the inventive concept, athree-dimensional semiconductor memory device includes an electrodestructure including a plurality of gate electrodes and a plurality ofinsulating layers, which are alternately stacked on a substrate. A sidesurface of the electrode structure is recessed in areas corresponding tothe gate electrodes to define a plurality of recess regions. Thethree-dimensional semiconductor memory device further includes asemiconductor pattern extending in a first direction substantiallyperpendicular to a top surface of the substrate and crossing the sidesurface of the electrode structure, a plurality of first charge traplayers, which are respectively disposed in the recess regions of theelectrode structure and surround the semiconductor pattern, a tunnelinsulating layer disposed between the first charge trap layers and thesemiconductor pattern, a blocking insulating layer disposed between thefirst charge trap layers and the electrode structure, and a secondcharge trap layer. The second charge trap layer continuously extendsbetween the blocking insulating layer and the first charge trap layersand between the tunnel insulating layer and the first charge traplayers. The first charge trap layers are formed of a material having afirst energy band gap, and the second charge trap layer is formed of amaterial having a second energy band gap larger than the first energyband gap.

According to exemplary embodiments of the inventive concept, athree-dimensional semiconductor memory device includes an electrodestructure including a plurality of gate electrodes and a plurality ofinsulating layers, which are alternately stacked on a substrate, asemiconductor pattern extending in a first direction substantiallyperpendicular to a top surface of the substrate and penetrating theelectrode structure, a tunnel insulating layer disposed between thesemiconductor pattern and the electrode structure, a blocking insulatinglayer disposed between the tunnel insulating layer and the electrodestructure, and a charge storing layer disposed between the blockinginsulating layer and the tunnel insulating layer. The charge storinglayer has a first thickness in first regions adjacent to the gateelectrodes, and a second thickness, which is less than the firstthickness, in second regions adjacent to the insulating layers. Thecharge storing layer includes a plurality of first charge trap layers,which are respectively disposed in the first regions, and a secondcharge trap layer. The first charge trap layers have a first energy bandgap, and the second charge trap layer has a second energy band gapgreater than the first energy band gap.

According to exemplary embodiments of the inventive concept, a chargestoring layer of a three-dimensional semiconductor memory deviceincludes a plurality of first charge trap layers having a first energyband gap, and a second charge trap layer having a second energy band gaplarger than the first energy band gap. The first charge trap layers areembedded in the second charge trap layer between gate electrodes of thethree-dimensional semiconductor memory device and a semiconductorpattern of the three-dimensional semiconductor memory device.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the inventive concept will become more apparentby describing in detail exemplary embodiments thereof with reference tothe accompanying drawings, in which:

FIG. 1 is a circuit diagram illustrating a cell array of athree-dimensional semiconductor memory device according to exemplaryembodiments of the inventive concept.

FIG. 2 is a plan view illustrating a cell array of a three-dimensionalsemiconductor memory device according to exemplary embodiments of theinventive concept.

FIGS. 3 and 4 are cross-sectional views illustrating three-dimensionalsemiconductor memory devices according to exemplary embodiments of theinventive concept, taken along line I-I′ of FIG. 2.

FIGS. 5A and 5B are diagrams illustrating a data storing structure of athree-dimensional semiconductor memory device according to exemplaryembodiments of the inventive concept.

FIGS. 6A and 6B are flat band diagrams illustrating energy bandstructures of three-dimensional semiconductor memory devices accordingto exemplary embodiments of the inventive concept.

FIGS. 7A and 7B are energy band diagrams referred to for describingcharge retention properties of three-dimensional semiconductor memorydevices according to exemplary embodiments of the inventive concept.

FIG. 8 is a cross-sectional view illustrating a three-dimensionalsemiconductor memory device according to exemplary embodiments of theinventive concept.

FIGS. 9A to 9H are cross-sectional views illustrating a portion of athree-dimensional semiconductor memory device according to exemplaryembodiments of the inventive concept (e.g., a portion A of FIG. 3, 4, or8).

FIGS. 10 to 15 are cross-sectional views taken along line I-I′ of FIG. 2illustrating a method of fabricating a three-dimensional semiconductormemory device according to exemplary embodiments of the inventiveconcept.

FIGS. 16 to 20 are cross-sectional views illustrating a method offorming vertical structures of a three-dimensional semiconductor memorydevice according to exemplary embodiments of the inventive concept.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Exemplary embodiments of the inventive concept will be described morefully hereinafter with reference to the accompanying drawings. Likereference numerals may refer to like elements throughout theaccompanying drawings.

Spatially relative terms, such as “beneath”, “below”, “lower”, “under”,“above”, “upper”, etc., may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” or“under” other elements or features would then be oriented “above” theother elements or features. Thus, the exemplary terms “below” and“under” can encompass both an orientation of above and below.

It will be understood that when a component, such as a film, a region, alayer, or an element, is referred to as being “on”, “connected to”,“coupled to”, or “adjacent to” another component, it can be directly on,connected, coupled, or adjacent to the other component, or interveningcomponents may be present. It will also be understood that when acomponent is referred to as being “between” two components, it can bethe only component between the two components, or one or moreintervening components may also be present. It will also be understoodthat when a component is referred to as “covering” another component, itcan be the only component covering the other component, or one or moreintervening components may also be covering the other component.

It will be understood that the terms “first,” “second,” “third,” etc.are used herein to distinguish one element from another, and theelements are not limited by these terms. Thus, a “first” element in anexemplary embodiment may be described as a “second” element in anotherexemplary embodiment.

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

It will be understood that when two components or directions aredescribed as extending substantially parallel or perpendicular to eachother, the two components or directions extend exactly parallel orperpendicular to each other, or extend approximately parallel orperpendicular to each other within a measurement error as would beunderstood by a person having ordinary skill in the art.

FIG. 1 is a circuit diagram illustrating a cell array of athree-dimensional semiconductor memory device according to exemplaryembodiments of the inventive concept.

Referring to FIG. 1, in an exemplary embodiment, a cell array of athree-dimensional semiconductor memory device includes a common sourceline CSL, a plurality of bit lines BL0-BL2, and a plurality of cellstrings CSTR disposed between the common source line CSL and the bitlines BL0-BL2BL.

The cell strings CSTR are disposed on a plane that is substantiallyparallel to first and second directions D1 and D2, extends in a thirddirection D3. The bit lines BL0-BL2 are spaced apart from one another inthe first direction D1 and extend in the second direction D2.

A plurality of the cell strings CSTR is connected substantially inparallel to each of the bit lines BL0-BL2. The plurality of the cellstrings CSTR is connected in common to the common source line CSL. Forexample, the plurality of the cell strings CSTR is disposed between thebit lines BL0-BL2 and the common source line CSL. A plurality of thecommon source lines CSL may be two-dimensionally arranged. The samevoltage may be applied to the common source lines CSL, or the commonsource lines CSL may be independently controlled.

In exemplary embodiments, each of the cell strings CSTR includes stringselection transistors SST1 and SST2, which are connected in series,memory cell transistors MCT, which are connected in series, and a groundselection transistor GST. Each of the memory cell transistors MCTincludes a data storage element.

As an example, each of the cell strings CSTR may include first andsecond string selection transistors SST1 and SST2, which are connectedin series, the second string selection transistors SST2 may be coupledto the bit lines BL0-BL2, and the ground selection transistor GST may becoupled to the common source line CSL. The memory cell transistors MCTmay be disposed between the first string selection transistor SST1 andthe ground selection transistor GST to be connected in series to oneanother.

In exemplary embodiments, each of the cell strings CSTR further includesa dummy cell DMC, which is provided between and connected to the firststring selection transistor SST1 and the memory cell transistor MCT.Another dummy cell may be disposed between and connected to the groundselection transistor GST and the memory cell transistor MCT. Inexemplary embodiments, in each of the cell strings CSTR, the groundselection transistor GST includes a plurality ofmetal-oxide-semiconductor (MOS) transistors, which are connected inseries, similar to the first and second string selection transistorsSST1 and SST2. In exemplary embodiments, each of the cell strings CSTRincludes a single string selection transistor.

In exemplary embodiments, the first string selection transistor SST1 iscontrolled by a first string selection line SSL1, and the second stringselection transistor SST2 is controlled by a second string selectionline SSL2. The memory cell transistors MCT are controlled by a pluralityof word lines WL0-WLn (where n is an integer equal to at least 2), andthe dummy cells DMC are controlled by a dummy word line DWL. The groundselection transistor GST is controlled by a ground selection line GSL.The common source line CSL is connected in common to sources of theground selection transistors GST.

In exemplary embodiments, each of the cell strings CSTR includes aplurality of the memory cell transistors MCT located at differentdistances from the common source lines CSL. The plurality of word linesWL0-WLn and the dummy word line DWL are disposed between the commonsource lines CSL and the bit lines BL0-BL2.

In exemplary embodiments, gate electrodes GE of the memory celltransistors MCT, which are placed at substantially the same distancefrom the common source lines CSL, are connected in common to one of theword lines WL0-WLn and DWL, thereby being in an equipotential state. Inexemplary embodiments, some of the gate electrodes GE of the memory celltransistors MCT, which are placed at substantially the same level fromthe common source lines CSL and are arranged in different rows orcolumn, may be independently controlled.

The ground selection lines GSL and the string selection lines SSL1 andSSL2 extend in the first direction D1, and are spaced apart from oneanother in the second direction D2. Although the ground selection linesGSL or the string selection lines SSL1 and SSL2 are located atsubstantially the same distance from the common source lines CSL, theymay be electrically separated from each other.

FIG. 2 is a plan view illustrating a cell array of a three-dimensionalsemiconductor memory device according to exemplary embodiments of theinventive concept. FIGS. 3 and 4 are cross-sectional views illustratingthree-dimensional semiconductor memory devices according to exemplaryembodiments of the inventive concept, taken along line I-I′ of FIG. 2.FIGS. 5A and 5B are diagrams illustrating a data storing structure of athree-dimensional semiconductor memory device according to exemplaryembodiments of the inventive concept. FIGS. 5A and 5B illustrate aportion of a three-dimensional semiconductor memory device according toexemplary embodiments of the inventive concept (e.g., a portion A ofFIG. 3, 4 or 8). FIGS. 6A and 6B are flat band diagrams illustratingenergy band structures of three-dimensional semiconductor memory devicesaccording to exemplary embodiments of the inventive concept.

Referring to FIGS. 2 and 3, in exemplary embodiments, electrodestructures ST are disposed on a top surface of a substrate 10. Theelectrode structures ST extend in the first direction D1 and are spacedapart from one another in the second direction D2, where the first andsecond directions D1 and D2 are orthogonal to each other and aresubstantially parallel to the top surface of the substrate 10.

The substrate 10 may include at least one of, for example, asemiconductor material (e.g., silicon), an insulating material (e.g.,glass), or a semiconductor or conductive material covered with aninsulating material. For example, the substrate 10 may be a siliconwafer having a first conductivity type.

A buffer insulating layer 11 is disposed between the electrode structureST and the substrate 10. The buffer insulating layer 11 may include, forexample, a silicon oxide layer.

The electrode structure ST includes gate electrodes GE and insulatinglayers ILD, which are alternately and repeatedly stacked on the topsurface of the substrate 10 in the third direction D3 normal to the topsurface. The gate electrodes GE may have substantially the samethickness, and the insulating layers ILD may have thicknesses that aredependent on the type of the semiconductor memory device. The gateelectrodes GE may be formed of or include at least one of, for example,doped semiconductors (e.g., doped silicon), metals (e.g., tungsten,copper, aluminum, etc.), conductive metal nitrides (e.g., titaniumnitride, tantalum nitride, etc.), or transition metals (e.g., titanium,tantalum, etc.). The insulating layers ILD may include, for example, asilicon oxide layer or a low-k dielectric layer. In exemplaryembodiments, the three-dimensional semiconductor memory device may bethe vertical-type NAND FLASH memory device described with reference toFIG. 1. In this case, the gate electrodes GE of the electrode structureST may be used as the ground selection lines GSL, the word lines WL0-WLnand DWL, and the string selection lines SSL1 and SSL2 described withreference to FIG. 1.

In exemplary embodiments, each of the gate electrodes GE has a sidesurface that is laterally offset from a side surface of the insulatinglayer ILD. For example, a side surface of the electrode structure STadjacent to a vertical structure VS may be disposed to define recessregions between vertically adjacent insulating layers ILD. As anexample, in exemplary embodiments, when measured in the first or seconddirection D1 or D2 substantially parallel to the top surface of thesubstrate 10, the side surfaces of the insulating layers ILD are spacedapart from a side surface of a semiconductor pattern SP (see FIG. 5A) bya first distance, whereas the side surfaces of the gate electrodes GEare spaced apart from the side surface of the semiconductor pattern SPby a second distance, which is larger than the first distance.

In exemplary embodiments, a plurality of the vertical structures VS isdisposed to extend in the third direction D3, which is normal to the topsurface of the substrate 10, and thereby penetrates a corresponding oneof the electrode structures ST. The vertical structures VS are arrangedto form a plurality of columns in the first direction D1. In exemplaryembodiments, the vertical structures VS are provided to form a zigzagarrangement in the first and second directions D1 and D2 when viewed ina plan view.

According to exemplary embodiments, each of the vertical structures VSincludes a channel structure CHS and a data storing structure DSS.

Referring to FIGS. 3 and 5A, in exemplary embodiments, the channelstructure CHS includes the semiconductor pattern SP and a buriedinsulating pattern VI. The semiconductor pattern SP of the channelstructure CHS may be in direct contact with the substrate 10, and maybe, for example, a U-shaped hollow pattern, or may be shaped like abottom-closed pipe or macaroni. An internal empty space of thesemiconductor pattern SP may be filled with the buried insulatingpattern VI. The semiconductor pattern SP may be formed of or include atleast one of, for example, semiconductor materials (e.g., silicon (Si),germanium (Ge), or mixtures thereof). In addition, the semiconductorpattern SP may be a doped semiconductor pattern or an intrinsicsemiconductor pattern. The semiconductor pattern SP may be used aschannel regions of the selection transistors SST and GST and the memorycell transistors MCT described with reference to FIG. 1.

Referring to FIG. 4, in an exemplary embodiment, each of the channelstructures CHS includes lower and upper semiconductor patterns LSP andUSP and the buried insulating pattern VI. The lower semiconductorpattern LSP may be in direct contact with the substrate 10 and mayinclude a pillar-shaped epitaxial layer grown from the substrate 10. Thelower semiconductor pattern LSP may be formed of, for example, silicon(Si), In exemplary embodiments, the lower semiconductor pattern LSP mayinclude at least one of germanium (Ge), silicon-germanium (SiGe), III-Vsemiconductor compounds, and/or II-VI semiconductor compounds. The lowersemiconductor pattern LSP may be, for example, an undoped pattern, ormay be a doped pattern having the same conductivity type as that of thesubstrate 10.

In exemplary embodiments, a top surface of the lower semiconductorpattern LSP is located at a level that is higher than a top surface ofthe lowermost one of the gate electrodes GE, and is lower than a bottomsurface of the lowermost insulating layer ILD on the lowermost one ofthe gate electrodes GE, as shown in FIG. 4. A gate insulating layer 15may be disposed on a portion of the side surface of the lowersemiconductor pattern LSP. The gate insulating layer 15 may be disposedbetween the lowermost one of the gate electrodes GE and the lowersemiconductor pattern LSP. The gate insulating layer 15 may include, forexample, a silicon oxide layer (e.g., a thermally-grown oxide layer).The gate insulating layer 15 may have a rounded side surface.

The upper semiconductor pattern USP may be in direct contact with thelower semiconductor pattern LSP, and may be shaped like a bottom-closedpipe or may be a ‘U’-shaped pattern. An internal space of the uppersemiconductor pattern USP may be filled with the buried insulatingpattern VI including an insulating material. The upper semiconductorpattern USP may be surrounded by the data storing structure DSS. Abottom surface of the upper semiconductor pattern USP may be located ata level that is lower than the top surface of the lower semiconductorpattern LSP. The upper semiconductor pattern USP may be formed of orinclude an undoped semiconductor material or a doped semiconductormaterial having substantially the same conductivity type as that of thesubstrate 10. In exemplary embodiments, the upper semiconductor patternUSP may have at least one of, for example, a single- or poly-crystallineor amorphous structure. In exemplary embodiments, the uppersemiconductor pattern USP may have a different crystal structure fromthat of the lower semiconductor pattern LSP.

In exemplary embodiments, a bit line conductive pad PAD, which is formedof a conductive material, is provided on or in a top portion of each ofthe channel structures CHS. As an example, the bit line conductive padPAD may be formed of a doped semiconductor material.

In exemplary embodiments, the data storing structure DSS is disposedbetween the channel structure CHS and the electrode structure ST. Thedata storing structure DSS extends in the third direction D3 andsurrounds the side surface of the channel structure CHS. The datastoring structure DSS may be used as a data storing layer in the NANDFLASH memory device, and may be configured in such a way that datastored therein can be changed using a voltage difference between thechannel structure CHS and the electrodes GE or using a Fowler-Nordheimtunneling effect caused by such a voltage difference.

Referring again to FIGS. 3 and 5A, in exemplary embodiments, the datastoring structure DSS includes first portions adjacent to the gateelectrodes GE and second portions adjacent to the insulating layers ILD.When measured in a direction normal to the side surface of the channelstructure CHS, a thickness t1 of the first portions is larger than athickness t2 of the second portions. The data storing structure DSSincludes a tunnel insulating layer TIL, a charge storing layer CS, and afirst blocking insulating layer BLK1.

The charge storing layer CS is disposed between the tunnel insulatinglayer TIL and the first blocking insulating layer BLK1. The chargestoring layer CS may be formed of or include at least one of materialswhose energy band gaps are less than those of the tunnel insulatinglayer TIL and the first blocking insulating layer BLK1.

Referring to FIGS. 5A and 6A, in exemplary embodiments, the chargestoring layer CS includes a first charge trap layer CT1 having a firstenergy band gap EG1 and a second charge trap layer CT2 having a secondenergy band gap EG2. In exemplary embodiments, the first charge traplayer CT1 is embedded in the second charge trap layer CT2. The firstenergy band gap EG1 is smaller than the second energy band gap EG2. Inaddition, the second energy band gap EG2 of the second charge trap layerCT2 is smaller than an energy band gap of the tunnel insulating layerTIL. A difference in conduction band energy level between the first andsecond charge trap layers CT1 and CT2 (hereinafter referred to as apotential barrier ΔE1) is greater than a difference in conduction bandenergy level between the tunnel insulating layer TIL and the secondcharge trap layer CT2 (hereinafter referred to as ΔE2). As an example,the first charge trap layer CT1 may be formed of or include, forexample, a poly-silicon layer, a germanium (Ge) layer, or a metal (e.g.,tungsten (W), nickel (Ni), platinum (Pt)) layer, and the second chargetrap layer CT2 may be formed of or include, for example, a siliconnitride layer or a silicon oxynitride layer.

Referring again to FIG. 5A, in exemplary embodiments, the charge storinglayer CS includes a plurality of patterns that are spaced apart from oneanother in the third direction D3. In exemplary embodiments, the chargestoring layer CS is not disposed between the insulating layers ILD andthe channel structure CHS. In exemplary embodiments, the first chargetrap layer CT1 of the charge storing layer CS surrounds a portion of thesemiconductor pattern SP adjacent to the gate electrode GE. In exemplaryembodiments, the second charge trap layer CT2 completely encloses (e.g.,completely surrounds) the first charge trap layer CT1. For example, thefirst charge trap layer CT1 may be covered by the second charge traplayer CT2 in all directions (e.g., the first, second, and thirddirections D1, D2, and D3). For example, in exemplary embodiments, thesecond charge trap layer CT2 includes vertical portions, which aredisposed between the tunnel insulating layer TIL and the first chargetrap layer CT1 and between the first blocking insulating layer BLK1 andthe first charge trap layer CT1, and horizontal portions, which areextended from the vertical portions to cover top and bottom surfaces ofthe first charge trap layer CT1. In exemplary embodiments, the secondcharge trap layer CT2 is thinner than the first charge trap layer CT1when measured in the first or second direction D1 or D2. Furthermore, inexemplary embodiments, the second charge trap layer CT2 is also thinnerthan the tunnel insulating layer TIL.

Various structures of the data storing structure DSS according toexemplary embodiments of the inventive concept will be described in moredetail with reference to FIGS. 9A to 9H.

Referring still to FIG. 5A, in exemplary embodiments, the tunnelinsulating layer TIL is disposed between the gate electrodes GE and thechannel structure CHS. The tunnel insulating layer TIL may be formed ofor include, for example, at least one of materials whose band gaps aregreater than that of the charge storing layer CS. The tunnel insulatinglayer TIL encloses the side surface of the semiconductor pattern SP,extends in the third direction D3, and may have a uniform thickness. Forexample, the tunnel insulating layer TIL may be a silicon oxide layer,which is formed by a chemical vapor deposition process or an atomiclayer deposition process. Alternatively, the tunnel insulating layer TILmay be formed of or include at least one of high-k dielectric materials(e.g., aluminum oxide and hafnium oxide).

Referring to FIGS. 5B and 6B, in exemplary embodiments, the tunnelinsulating layer TIL includes a plurality of thin layers. For example,as shown in FIG. 5B, in an exemplary embodiment, the tunnel insulatinglayer TIL includes first, second, and third tunnel insulating layersTILL TIL2, and TIL3, which are sequentially stacked on the side surfaceof the channel structure CHS. The second tunnel insulating layer TIL2has an energy band gap that is smaller than those of the first and thirdtunnel insulating layers TIL1 and TIL3, as shown in FIG. 6B. Since thesecond tunnel insulating layer TIL2 having a small energy band gap isdisposed between the first and third tunnel insulating layers TIL1 andTIL3, the tunnel insulating layer TIL may allow holes to be more easilytunneled during an erase operation of the three-dimensionalsemiconductor memory device.

The first and second tunnel insulating layers TIL1 and TIL2 may beformed of or include, for example, a nitrogen-containing material (e.g.,silicon nitride or silicon oxynitride). The third tunnel insulatinglayer TIL3 may be formed of or include, for example, silicon oxide.

In exemplary embodiments, the first blocking insulating layer BLK1 isdisposed between the gate electrodes GE and the tunnel insulating layerTIL, and may be formed of or include, for example, at least one ofmaterials whose band gaps are smaller than that of the tunnel insulatinglayer TIL and are greater than that of the charge storing layer CS. Aneffective dielectric constant of the first blocking insulating layerBLK1 may be greater than that of the tunnel insulating layer TIL. Forexample, the first blocking insulating layer BLK1 may be formed of orinclude at least one of, for example, high-k dielectric materials (e.g.,aluminum oxide and hafnium oxide). In exemplary embodiments, the firstblocking insulating layer BLK1 has a substantially uniform thickness andextends in the third direction D3. In exemplary embodiments, the firstblocking insulating layer BLK1 is in contact with the tunnel insulatinglayer TIL between vertically adjacent gate electrodes GE, and surroundsthe charge storing layer CS between vertically adjacent insulatinglayers ILD.

In addition, in exemplary embodiments, a second blocking insulatinglayer BLK2 is disposed between the channel structures CHS and the sidesurfaces of the gate electrodes GE, and extends to cover top and bottomsurfaces of each of the gate electrodes GE. The second blockinginsulating layer BLK2 may be, for example, a single layer or a pluralityof thin layers. The second blocking insulating layer BLK2 may be formedof or include, for example, at least one of high-k dielectric materials(e.g., aluminum oxide and hafnium oxide). In exemplary embodiments, thesecond blocking insulating layer BLK2 is formed of or includes at leastone of materials whose dielectric constants are different from that ofthe first blocking insulating layer BLK1. In exemplary embodiments, thesecond blocking insulating layer BLK2 is omitted.

In the figures, BLK may collectively refer to the first blockinginsulating layer BLK1 and the second blocking insulating layer BLK2. Asshown in FIG. 5A, in exemplary embodiments, the second charge trap layerCT2 continuously extends (e.g., extends without any breaks or openings)between the blocking insulating layer BLK and the first charge traplayer CT1, and continuously extends between the tunnel insulating layerTIL and the first charge trap layer CT1.

Referring again to FIGS. 2 and 3, in exemplary embodiments, commonsource regions CSR are disposed in the substrate 10 and between theelectrode structures ST. The common source regions CSR extend in thefirst direction D1 or substantially parallel to the electrode structuresST, and are spaced apart from one another in the second direction D2.For example, each of the electrode structures ST is disposed betweenadjacent common source regions CSR. In exemplary embodiments, the commonsource regions CSR may be formed by injecting impurities having a secondconductivity type into the substrate 10, which has the firstconductivity type different from the second conductivity type. Forexample, the common source regions CSR may be formed to contain n-typeimpurities (e.g., arsenic (As) or phosphorus (P)).

In exemplary embodiments, a first interlayered insulating layer 50 isdisposed on the electrode structures ST, and covers the top surfaces ofthe vertical structures VS.

In exemplary embodiments, a common source plug CSP is disposed betweenthe electrode structures ST and is coupled to the common source regionCSR, and an insulating spacer SS is disposed between the common sourceplug CSP and the side surfaces of the electrode structures ST. As anexample, the common source plug CSP may be formed to have asubstantially uniform upper width, and may extend in the first directionD1.

In exemplary embodiments, a second interlayered insulating layer 60 isdisposed on the first interlayered insulating layer 50, and covers a topsurface of the common source plug CSP.

In exemplary embodiments, bit lines BL, which include the bit linesBL0-BL2, extend in the second direction D2, are disposed on the secondinterlayered insulating layer 60, and cross the electrode structures ST.The bit lines BL may be coupled to the bit line conductive pads PADthrough bit line contact plugs BPLG. For example, the bit lines BL areelectrically connected to the channel structures CHS.

FIGS. 7A and 7B are energy band diagrams referred to for describingcharge retention properties of three-dimensional semiconductor memorydevices according to exemplary embodiments of the inventive concept.FIG. 7A is a diagram illustrating an energy band structure in adirection substantially parallel to the top surface of the substrate,and FIG. 7B is a diagram illustrating an energy band structure in adirection substantially perpendicular to the top surface of thesubstrate.

In a three-dimensional semiconductor memory device according toexemplary embodiments of the inventive concept, during a programmingoperation, electric charges in the semiconductor pattern SP of thechannel structure may pass through the tunnel insulating layer TIL by aFowler-Nordheim tunneling and may be trapped in the charge storing layerCS. The electric charges, which are trapped in the charge storing layerCS (e.g., the first and second charge trap layers CT1 and CT2), maychange a threshold voltage of a memory cell transistor.

During the programming operation, a high voltage may be selectivelyapplied to one of the gate electrodes GE. In this case, since the firstcharge trap layer CT1 has an energy band gap smaller than that of thesecond charge trap layer CT2, it is likely that electric charges, whichhave tunneled through the tunnel insulating layer TIL, are trapped inthe first charge trap layer CT1 having a deep trap level.

In the three-dimensional semiconductor memory device according toexemplary embodiments of the inventive concept, once the electriccharges are stored in the first and second charge trap layers CT1 andCT2, the program voltage applied to the gate electrode GE may beinterrupted to allow the device to be operated in a charge retentionmode.

Referring to FIG. 7A, in exemplary embodiments, the charge storing layerCS has a deformed or curved energy band structure, owing to the chargestrapped in the charge storing layer CS in the charge retention mode.According to exemplary embodiments, a potential barrier between thefirst and second charge trap layers CT1 and CT2 is greater than thatbetween the tunnel insulating layer TIL and the second charge trap layerCT2. As a result, it exemplary embodiments reduce an amount of electriccharges, which are thermally excited to the conduction band of the firstcharge trap layer CT1 in the charge retention mode and surmount thepotential barrier between the first and second charge trap layers CT1and CT2 to be leaked to the semiconductor pattern SP. Furthermore, evenif electric charges trapped in a shallow trap level (e.g., close to theconduction band) of the second charge trap layer CT2 are thermallyexcited, the excited electric charges may be re-trapped in the firstcharge trap layer CT1 because the first charge trap layer CT1 has aconduction band energy level lower than that of the second charge traplayer CT2.

In addition, since the second charge trap layer CT2 encloses the firstcharge trap layer CT1, exemplary embodiments suppress or prevent theelectric charges, which are trapped in the first charge trap layer CT1,from being leaked to the semiconductor pattern SP through the tunnelinsulating layer TIL by a band-to-band tunneling.

Referring to FIG. 7B, in exemplary embodiments, the first charge traplayer CT1 is not extended toward the insulating layers ILD between thegate electrodes GE. For example, the first charge trap layer CT1 may belocally formed, and thus, electric charges trapped in the first chargetrap layer CT1 may be prevented from being diffused in a verticaldirection normal to the top surface of the substrate.

Thus, exemplary embodiments of the inventive concept prevent electriccharges from being lost in all directions substantially parallel andsubstantially perpendicular to the top surface of the substrate in thecharge retention mode. As a result, a charge retention property of athree-dimensional semiconductor memory device may be improved accordingto exemplary embodiments of the inventive concept.

FIG. 8 is a cross-sectional view illustrating a three-dimensionalsemiconductor memory device according to exemplary embodiments of theinventive concept. For convenience of explanation, elements previouslydescribed may be identified by the same reference numerals, and afurther description thereof may be omitted.

Referring to FIG. 8, in exemplary embodiments, the electrode structuresST are disposed on the substrate 10 and are spaced apart from oneanother, and a plurality of the vertical structures VS are disposed suchthat they penetrate each of the electrode structure ST. Each of thevertical structures VS includes the channel structure CHS and the datastoring structure DSS.

In exemplary embodiments, the channel structure CHS includes first andsecond vertical channels VS1 and VS2 which penetrate the electrodestructure ST, and a horizontal channel HS which is disposed below theelectrode structure ST and connects the first and second verticalchannels VS1 and VS2 to each other. The first and second verticalchannels VS1 and VS2 may be disposed in vertical holes that are formedto penetrate the electrode structure ST. The horizontal channel HS maybe provided in a recess region formed in the substrate 10. Thehorizontal channel HS is disposed between the substrate 10 and theelectrode structure ST and connects the first and second verticalchannels VS1 and VS2 to each other. In exemplary embodiments, thehorizontal channel HS may be, for example, a hollow pipe shaped or amacaroni-shaped pattern, which is continuously connected to the firstand second vertical channels VS1 and VS2. For example, in exemplaryembodiments, the first and second vertical channels VS1 and VS2 and thehorizontal channel HS are disposed such that they have a single pipestructure. For example, the first and second vertical channels VS1 andVS2 and the horizontal channel HS may be a single continuoussemiconductor layer without interface.

In exemplary embodiments, in each of the channel structures CHS, thefirst vertical channel VS1 is connected to a bit line BL, and the secondvertical channel VS2 is connected to the common source line CSL. In thiscase, each of the channel structures CHS may be used as channel regionsof memory cell transistors and ground and string selection transistorsconstituting a single cell string.

Furthermore, as described above, in exemplary embodiments, the datastoring structure DSS is disposed between the first and second verticalchannels VS1 and VS2 and the electrode structures ST and between thehorizontal channel HS and the substrate 10.

FIGS. 9A to 9H are cross-sectional views illustrating a portion of athree-dimensional semiconductor memory device according to exemplaryembodiments of the inventive concept (e.g., a portion A of FIG. 3, 4, or8).

According to exemplary embodiments, the data storing structure DSSincludes first portions adjacent to the gate electrodes GE, and secondportions adjacent to the insulating layers ILD. The first portions arethicker than the second portions. For example, in exemplary embodiments,a thickness of the data storing structure DSS is larger in an areabetween the side surfaces of the gate electrodes GE and the channelstructure CHS than in an area between the side surfaces of theinsulating layers ILD and the channel structure CHS. As an example, inexemplary embodiments, a distance from the side surface of thesemiconductor pattern SP to the side surface of the gate electrode GE islarger than a distance from the side surface of the semiconductorpattern SP to the side surface of the insulating layer ILD.

In exemplary embodiments, the data storing structure DSS includes thetunnel insulating layer TIL, the charge storing layer CS, and the firstblocking insulating layer BLK1, which are sequentially stacked on theside surface of the channel structure CHS. As described above, inexemplary embodiments, the charge storing layer CS includes the firstcharge trap layer CT1 and the second charge trap layer CT2 having thefirst energy band gap and the second energy band gap, respectively. Thefirst energy band gap is smaller than the second energy band gap. Inexemplary embodiments, the tunnel insulating layer TIL and the firstblocking insulating layer BLK1 extend in a direction normal to the topsurface of the substrate (e.g., in the third direction D3 of FIG. 3).

Referring to FIGS. 9A and 9B, in exemplary embodiments, the chargestoring layer CS includes a plurality of patterns, which are spacedapart from one another in the third direction D3, and each of whichsurrounds a portion of the channel structure. In such exemplaryembodiments, the charge storing layer CS may not be disposed between theinsulating layers ILD and the channel structure CHS.

Referring to FIG. 9A, in exemplary embodiments, the first charge traplayer CT1 surrounds a portion of the semiconductor pattern SP adjacentto the gate electrode GE, and is in direct contact with the tunnelinsulating layer TIL. The second charge trap layer CT2 is disposedbetween the first blocking insulating layer BLK1 and the first chargetrap layer CT1, and includes portions covering top and bottom surfacesof the first charge trap layer CT1.

Referring to FIG. 9B, in exemplary embodiments, the first charge traplayer CT1 is disposed such that it is in contact with the first blockinginsulating layer BLK1, and the second charge trap layer CT2 is disposedsuch that it is in contact with the tunnel insulating layer TIL. Top andbottom surfaces of each of the first and second charge trap layers CT1and CT2 are in contact with the first blocking insulating layer BLK1.

Referring to FIGS. 9C to 9G, in exemplary embodiments, the first chargetrap layer CT1 includes a plurality of patterns, which are spaced apartfrom one another in the third direction D3, and the second charge traplayer CT2 extends in the third direction D3. For example, in exemplaryembodiments, each of the patterns of the first charge trap layer CT1 islocally provided between vertically adjacent insulating layers ILD, andsurround a portion of the channel structure CHS. In exemplaryembodiments, the first charge trap layer CT1 is not disposed between theinsulating layers ILD and the channel structure CHS.

Referring to FIG. 9C, in exemplary embodiments, the second charge traplayer CT2 extends in the third direction D3, and completely surroundseach of the patterns of the first charge trap layer CT1. For example, ina region adjacent to the insulating layers ILD, the second charge traplayer CT2 is disposed between the first blocking insulating layer BLK1and the tunnel insulating layer TIL. The second charge trap layer CT2 isextended from a region between the insulating layers ILD and thesemiconductor pattern to a region between the first blocking insulatinglayer BLK1 and the first charge trap layer CT1, and to a region betweenthe tunnel insulating layer TIL and the first charge trap layer CT1.

Referring to FIG. 9D, in exemplary embodiments, the first charge traplayer CT1 is disposed such that it surrounds a portion of the channelstructure CHS, and is disposed between the first blocking insulatinglayer BLK1 and the second charge trap layer CT2. Furthermore, top andbottom surfaces of the first charge trap layer CT1 are in contact withthe first blocking insulating layer BLK1.

In exemplary embodiments, the second charge trap layer CT2 has a uniformthickness on the tunnel insulating layer TIL. The second charge traplayer CT2 extends in the third direction D3, thereby being disposedbetween the tunnel insulating layer TIL and the first charge trap layerCT1 and between the tunnel insulating layer TIL and the insulatinglayers ILD.

Referring to FIG. 9E, in exemplary embodiments, the first charge traplayer CT1 is disposed between the tunnel insulating layer TIL and thesecond charge trap layer CT2, and top and bottom surfaces of the firstcharge trap layer CT1 are in contact with the second charge trap layerCT2.

The second charge trap layer CT2 extends in the third direction D3 andincludes portions that are located between the first blocking insulatinglayer BLK1 and the first charge trap layer CT1, and between theinsulating layers ILD and the tunnel insulating layer TIL.

Referring to FIGS. 9F, 9G, and 9H, in exemplary embodiments, thesemiconductor pattern SP of the channel structure CHS includesprotruding portions laterally extending toward the gate electrodes GE.

Referring to FIG. 9F, in exemplary embodiments, the tunnel insulatinglayer TIL includes a plurality of patterns, which are spaced apart fromone another in the third direction D3, and each of which is in contactwith a side surface of each of vertically separated patterns of thefirst charge trap layer CT1. The first charge trap layer CT1 is disposedbetween the tunnel insulating layer TIL and the second charge trap layerCT2. The second charge trap layer CT2 extends from a region between thefirst blocking insulating layer BLK1 and the first charge trap layer CT1to a region between the insulating layers ILD and the channel structureCHS. The second charge trap layer CT2 is disposed such that it is incontact with top and bottom surfaces of the first charge trap layer CT1and the tunnel insulating layer TIL.

Referring to FIG. 9G, in exemplary embodiments, the first blockinginsulating layer BLK1 is disposed between the first charge trap layerCT1 and the gate electrode GE, and extends such that it covers the topand bottom surfaces of the first charge trap layer CT1. Furthermore, thefirst blocking insulating layer BLK1 extends in the third direction D3such that it is disposed between the insulating layers ILD and thechannel structure CHS.

In exemplary embodiments, each of the tunnel insulating layer TIL andthe second charge trap layer CT2 is disposed between the channelstructure CHS and the first blocking insulating layer BLK1, and extendsin the third direction D3 to surround the protruding portions of thechannel structure CHS.

Referring to FIG. 9H, in exemplary embodiments, the first blockinginsulating layer BLK1 and the second charge trap layer CT2 are disposedbetween the gate electrode GE and the first charge trap layer CT1. Thesecond charge trap layer CT2 covers bottom and top surfaces of the firstcharge trap layer CT1, and extends in the third direction D3 such thatit is disposed between the insulating layers ILD and the tunnelinsulating layer TIL.

In exemplary embodiments, the tunnel insulating layer TIL is in directcontact with a side surface of the first charge trap layer CT1, andextends in the third direction D3 such that it is disposed between thechannel structure CHS and the second charge trap layer CT2. In addition,in exemplary embodiments, the tunnel insulating layer TIL conformallycovers the protruding portions of the channel structure CHS. Forexample, the tunnel insulating layer TIL may have a shape correspondingto that of the protruding portions of the channel structure CHS in areasin which the tunnel insulating layer TIL covers the protruding portions.

FIGS. 10 to 15 are cross-sectional views taken along line I-I′ of FIG. 2illustrating a method of fabricating a three-dimensional semiconductormemory device according to exemplary embodiments of the inventiveconcept.

Referring to FIGS. 2 and 10, in exemplary embodiments, the bufferinsulating layer 11 is formed on the substrate 10, and then, a moldstructure 100 is formed on the buffer insulating layer 11. The moldstructure 100 may be formed by alternately and repeatedly stackingsacrificial layers SL and insulating layers ILD on the buffer insulatinglayer 11.

In the mold structure 100, the sacrificial layers SL may be formed of amaterial that can be selectively etched with respect to the insulatinglayers ILD. For example, materials for the sacrificial layers SL and theinsulating layers ILD may be selected to have a high etch selectivity ina wet etching process and a low etch selectivity in a dry etchingprocess. As an example, the sacrificial layers SL and the insulatinglayers ILD may be formed of insulating materials that have an etchselectivity with respect to each other. In exemplary embodiments, thesacrificial layers SL may be formed of an insulating material differentfrom the insulating layers ILD. For example, the sacrificial layers SLmay be formed of at least one selected from the group of silicon,silicon oxide, silicon carbide, silicon germanium, silicon oxynitride,or silicon nitride, whereas the insulating layers ILD may be formed ofat least one that is selected from the group but is different from thatof the sacrificial layers SL. As an example, in exemplary embodiments,the sacrificial layers SL are formed of silicon nitride, and theinsulating layers ILD are formed of silicon oxide. In exemplaryembodiments, the sacrificial layers SL are formed of a conductivematerial, and the insulating layers ILD are formed of an insulatingmaterial.

The sacrificial layers SL and the insulating layers ILD may be depositedusing at least one of, for example, thermal chemical vapor deposition(thermal CVD), plasma-enhanced CVD, physical CVD, or atomic layerdeposition (ALD) methods.

Thereafter, a plurality of vertical holes VH are formed to penetrate themold structure 100. The formation of the vertical holes VH may include,for example, forming a mask pattern on the mold structure 100 andanisotropically etching the mold structure 100 using the mask pattern asan etch mask. The anisotropic etching process may be performed to etchthe top surface of the substrate 10 in an over-etching manner, and thus,the top surface of the substrate 10 exposed by the vertical holes VH maybe recessed to a specific depth. Furthermore, as a result of theanisotropic etching process, the vertical holes VH may be formed to havea lower width that is smaller than an upper width. In addition, whenviewed in a plan view, the vertical holes VH may be arranged in a lineor in a zigzag shape.

Referring to FIGS. 2 and 11, in exemplary embodiments, the sacrificiallayers SL exposed by the vertical holes VH are laterally recessed toform recess regions RS between vertically adjacent insulating layersILD. The recess regions RS may be formed to have a diameter that islarger than that of the vertical holes VH. The recess regions RS may beformed by isotropically and partially etching the sacrificial layers SLusing an etch recipe having an etch selectivity with respect to theinsulating layers ILD. For example, in a case in which the sacrificiallayers SL are formed of silicon nitride and the insulating layers ILDare formed of silicon oxide, the recess regions RS may be formed by anisotropic etching process in which an etching solution containingphosphoric acid is used. In exemplary embodiments, the recess regions RSare formed in a side surface of the electrode structure ST in areascorresponding to the gate electrodes GE, and the first charge trap layerCT1 is formed in the recess regions RS. For example, in exemplaryembodiments, the recess regions RS are formed in a side surface of theelectrode structure ST toward the gate electrodes GE.

Referring to FIGS. 2 and 12, in exemplary embodiments, the verticalstructures VS are formed in the recess regions RS and the vertical holesVH. The formation of the vertical structures VS may include forming thedata storing structure DSS in the recess regions RS and the verticalholes VH, forming the channel structure CHS, and forming the bit lineconductive pad PAD in or on a top portion of the channel structure CHS.The vertical structures VS may be formed to be thicker near thesacrificial layers SL than near the insulating layers ILD. A method offorming the vertical structures VS will be described in more detail withreference to FIGS. 16 to 20.

Referring to FIGS. 2 and 13, in exemplary embodiments, after theformation of the vertical structures VS, the first interlayeredinsulating layer 50 is formed on the mold structure 100. The firstinterlayered insulating layer 50 covers top surfaces of the verticalstructures VS. Thereafter, the first interlayered insulating layer 50and the mold structure 100 may be patterned to form trenches T exposingthe substrate 10. As a result of the formation of the trenches T, themold structure 100 may be patterned to have a line shape extending in adirection.

In exemplary embodiments, the trenches T are formed such that they arespaced apart from the vertical structures VS, and expose side surfacesof the sacrificial and insulating layers SL and ILD. Each of thetrenches T may be formed to have a line or rectangular shape extendingin the first direction D1 when viewed in a plan view, and to expose thetop surface of the substrate 10 when viewed in a cross-sectional view.The trenches T may be formed in an over-etching manner, and thus, thetop surface of the substrate 10 exposed by the trenches T may berecessed to a specific depth. Furthermore, the trenches T may be formedusing an anisotropic etching process, but may have a side surface thatis inclined at an angle toward the top surface of the substrate 10.

Thereafter, the sacrificial layers SL exposed by the trenches T areremoved to form gate regions GR between the insulating layers ILD. Thegate regions GR may be formed, for example, by isotropically etching thesacrificial layers SL using an etch recipe having an etch selectivitywith respect to the buffer insulating layer 11, the insulating layersILD, the vertical structures VS, and the substrate 10. In exemplaryembodiments, the sacrificial layers SL may be completely removed by theisotropic etching process. For example, in a case in which thesacrificial layers SL are formed of silicon nitride and the insulatinglayers ILD are formed of silicon oxide, the recess regions RS may beformed by an isotropic etching process using an etching solutioncontaining phosphoric acid.

Furthermore, each of the gate regions GR may be an empty spacehorizontally extended from the trench T and located between theinsulating layers ILD, and may be formed to expose a portion of a sidesurface of the data storing structure DSS. For example, in exemplaryembodiments, each of the gate regions GR is an empty space defined by anadjacent pair of the insulating layers ILD and the side surface of thedata storing structure DSS.

Referring to FIGS. 2 and 14, in exemplary embodiments, the secondblocking insulating layer BLK2 is formed to conformally cover innersurfaces of the gate regions GR. For example, the second blockinginsulating layer BLK2 may be formed to have a substantially uniformthickness on the inner surfaces of the gate regions GR. The secondblocking insulating layer BLK2 may be composed of a single layer or aplurality of layers.

The gate electrodes GE are formed in the gate regions GR covered withthe second blocking insulating layer BLK2. Each of the gate electrodesGE may be formed to partially or completely fill a corresponding one ofthe gate regions GR.

The formation of the gate electrodes GE may include, for example,forming a gate conductive layer to fill the gate regions provided withthe second blocking insulating layer BLK2 and then removing the gateconductive layer from the trenches T to localize the gate electrodes GEin the gate regions, respectively. Each of the gate electrodes GE mayinclude a barrier metal layer and a metal layer that are sequentiallydeposited. The barrier metal layer may be formed of or include at leastone of metal nitride materials (e.g., TiN, TaN, and WN). The metal layermay be formed of or include at least one of metallic materials (e.g., W,Al, Ti, Ta, Co, and Cu).

As a result of the formation of the gate electrodes GE, the electrodestructures ST may be formed on the substrate 10. Each of the electrodestructures ST include the insulating layers ILD and the gate electrodesGE, which are alternately stacked on the substrate 10. The electrodestructures ST extend in the first direction D1, and side surfaces of theelectrode structures ST are exposed by the trench T. In addition, thesubstrate 10 is exposed between adjacent electrode structures ST whenviewed in a plan view.

Referring to FIGS. 2 and 15, in exemplary embodiments, the common sourceregions CSR are formed in portions of the substrate 10 exposed throughthe trenches T. The common source regions CSR extend in the firstdirection D1, extend substantially parallel to one another, and arespaced apart from one another in the second direction D2. For example,in exemplary embodiments, the common source regions CSR are formed inthe substrate 10 and between the electrode structures ST. The commonsource regions CSR may be formed, for example, by doping impurities,whose conductivity type is different from that of the substrate 10, intothe substrate 10. In exemplary embodiments, the common source regionsCSR contain n-type impurities (e.g., arsenic (As) or phosphorus (P)).

In exemplary embodiments, the insulating spacer SS is formed to coverside surfaces of the trenches T. The formation of the insulating spacerSS may include conformally depositing a spacer layer on the substrate 10provided with the electrode structures ST, and then performing anetch-back process on the spacer layer to expose the common source regionCSR. The spacer layer may be formed of at least one of insulatingmaterials (e.g., silicon oxide, silicon nitride, silicon oxynitride, orlow-k dielectric materials).

In exemplary embodiments, the common source plug CSP is formed in eachof the trenches T with the insulating spacer SS. The common source plugCSP extends substantially parallel to the gate electrodes GE.

Next, as shown in FIG. 3, the second interlayered insulating layer 60 isformed on the first interlayered insulating layer 50 to cover the topsurface of the common source plug CSP. Thereafter, the bit line contactplugs BPLG are formed to penetrate the first and second interlayeredinsulating layers 50 and 60, and to be coupled to the bit lineconductive pads PAD. Next, the bit lines BL are formed on the secondinterlayered insulating layer 60. The bit lines BL extend in the seconddirection D2 and are coupled to the bit line contact plugs BPLG.

FIGS. 16 to 20 are cross-sectional views illustrating a method offorming vertical structures of a three-dimensional semiconductor memorydevice according to exemplary embodiments of the inventive concept.FIGS. 16 to 20 correspond to a portion B of FIG. 15.

Referring to FIG. 16, as described above, in exemplary embodiments, thevertical holes VH are formed to penetrate the mold structure 100, andthen the recess regions RS are formed by recessing the side surfaces ofthe sacrificial layers SL. The recess regions RS are formed to have adiameter that is larger than that of the vertical holes VH. The topsurface of the substrate 10 may be vertically recessed during theformation of the vertical holes VH, and thus, a bottom surface of thevertical hole VH may be positioned at a level lower than that of the topsurface of the substrate 10.

Referring to FIG. 17, in exemplary embodiments, a first preliminaryblocking insulating layer 111, a second preliminary charge trap layer113, and a first preliminary charge trap layer 115 are formed tosequentially cover inner surfaces of the vertical holes VH and therecess regions RS. In exemplary embodiments, a sum of thicknesses of thefirst preliminary blocking insulating layer 111, the second preliminarycharge trap layer 113, and the first preliminary charge trap layer 115is smaller than about half the diameter of the vertical holes VH.

In exemplary embodiments, the first preliminary blocking insulatinglayer 111 and the second preliminary charge trap layer 113 are formed toconformally cover the inner surfaces of the vertical holes VH and therecess regions RS (e.g., with a uniform thickness). The firstpreliminary charge trap layer 115 may be formed to fill the recessregions RS on which the first preliminary blocking insulating layer 111and the second preliminary charge trap layer 113 are disposed.

Referring to FIG. 18, in exemplary embodiments, an anisotropic etchingprocess is performed on the first preliminary charge trap layer 115, thesecond preliminary charge trap layer 113, and the first preliminaryblocking insulating layer 111, which are formed in the vertical holesVH, thereby forming penetration holes exposing the top surface of thesubstrate 10 through the vertical holes VH. As a result of the formationof the penetration holes, the first blocking insulating layer BLK1, asecond charge trap layer CT2 a, and a plurality of first charge traplayers CT1 are formed. The first charge trap layers CT1 may be locallyformed in the recess regions RS, and may be spaced apart from oneanother in a direction substantially perpendicular to the top surface ofthe substrate 10.

In exemplary embodiments, a method of isotropically etching the firstpreliminary charge trap layer 115 is used to locally form the firstcharge trap layers CT1 in the recess regions RS. In this case, sidesurfaces of the first charge trap layers CT1 may be horizontallyrecessed compared with a side surface of the second charge trap layerCT2 a.

Referring to FIG. 19, in exemplary embodiments, a third preliminarycharge trap layer 121, a preliminary tunnel insulating layer 123, and afirst semiconductor layer 125 are sequentially deposited to conformallycover inner surfaces of the vertical holes VH, in which the firstblocking insulating layer BLK1, the second charge trap layer CT2 a, andthe first charge trap layers CT1 are disposed. The third preliminarycharge trap layer 121, the preliminary tunnel insulating layer 123, andthe first semiconductor layer 125 may define an empty space in each ofthe vertical holes VH. The third preliminary charge trap layer 121 maybe formed of or include the same material as the second charge traplayer CT2 a. In exemplary embodiments, a process of depositing the thirdpreliminary charge trap layer 121 is omitted, before the deposition ofthe preliminary tunnel insulating layer 123. In exemplary embodiments,the preliminary tunnel insulating layer 123 is formed by performing athermal oxidation process on the first charge trap layers CT1.

Thereafter, in exemplary embodiments, an anisotropic etching process isperformed on the third preliminary charge trap layer 121, thepreliminary tunnel insulating layer 123, and the first semiconductorlayer 125 to expose the substrate 10. As a result, a third charge traplayer CT2 b, the tunnel insulating layer TIL, and a first semiconductorpattern SP1 may be formed, as shown in FIG. 20.

Referring to FIG. 20, in exemplary embodiments, a second semiconductorlayer SP2 is deposited to conformally cover a side surface of the firstsemiconductor pattern SP1 and the substrate 10, and an empty spacedefined by the second semiconductor layer SP2 is filled with the buriedinsulating pattern VI.

According to exemplary embodiments of the inventive concept, a chargestoring layer adjacent to gate electrodes includes first and secondcharge trap layers having different energy band gaps. As a result,exemplary embodiments prevent or suppress electric charges, which aretrapped in the charge storing layer, from being spread in a horizontaldirection substantially parallel to a top surface of a substrate.Furthermore, according to exemplary embodiments, a data storingstructure is configured to include first charge trap layers, which havea deep trap level and are spaced apart from one another in a directionsubstantially perpendicular to the top surface of the substrate. As aresult, exemplary embodiments prevent or suppress electric charges,which are trapped in the charge storing layer, from being spread in avertical direction substantially perpendicular to the top surface of thesubstrate. For example, a three-dimensional semiconductor memory deviceaccording to exemplary embodiments of the inventive concept prevents orsuppresses electric charges, which are trapped in the charge storinglayer, from being spread in the vertical and horizontal directions.Accordingly, exemplary embodiments reduce loss of electric chargestrapped in the charge storing layer, and thereby may improve a chargeretention property of a three-dimensional semiconductor memory device.As a result, a three-dimensional semiconductor memory device withimproved reliability is provided.

According to exemplary embodiments of the inventive concept, a threedimensional (3D) memory array is provided. The 3D memory array ismonolithically formed in one or more physical levels of arrays of memorycells having an active area disposed above a silicon substrate andcircuitry associated with the operation of those memory cells, whethersuch associated circuitry is above or within such substrate. The term“monolithic” means that layers of each level of the array are directlydeposited on the layers of each underlying level of the array.

According to exemplary embodiments of the inventive concept, the 3Dmemory array includes vertical NAND strings that are vertically orientedsuch that at least one memory cell is located over another memory cell.The at least one memory cell may include a charge trap layer.

The following patent documents, which are hereby incorporated byreference, describe suitable configurations for three-dimensional memoryarrays, in which the three-dimensional memory array is configured as aplurality of levels, with word lines and/or bit lines shared betweenlevels: U.S. Pat. Nos. 7,679,133; 8,553,466; 8,654,587; 8,559,235; andUS Pat. Pub. No. 2011/0233648.

While the present inventive concept has been particularly shown anddescribed with reference to the exemplary embodiments thereof, it willbe understood by those of ordinary skill in the art that variations inform and detail may be made therein without departing from the spiritand scope of the present inventive concept as defined by the followingclaims.

1. A three-dimensional semiconductor memory device, comprising: anelectrode structure comprising a plurality of gate electrodes and aplurality of insulating layers, wherein the gate electrodes and theinsulating layers are alternately stacked on a substrate; asemiconductor pattern extending in a first direction substantiallyperpendicular to a top surface of the substrate and penetrating theelectrode structure; a tunnel insulating layer disposed between thesemiconductor pattern and the electrode structure; a blocking insulatinglayer disposed between the tunnel insulating layer and the electrodestructure; and a charge storing layer disposed between the blockinginsulating layer and the tunnel insulating layer, wherein the chargestoring layer comprises: a plurality of first charge trap layers havinga first energy band gap; and a second charge trap layer having a secondenergy band gap larger than the first energy band gap, wherein the firstcharge trap layers are embedded in the second charge trap layer betweenthe gate electrodes and the semiconductor pattern.
 2. Thethree-dimensional semiconductor memory device of claim 1, wherein sidesurfaces of the insulating layers are spaced apart from a side surfaceof the semiconductor pattern by a first distance in a second directionsubstantially parallel to the top surface of the substrate, and sidesurfaces of the gate electrodes are spaced apart from the side surfaceof the semiconductor pattern by a second distance in the seconddirection, wherein the second distance is larger than the firstdistance.
 3. The three-dimensional semiconductor memory device of claim2, wherein the charge storing layer has a first thickness between thegate electrodes and the semiconductor pattern in the second direction,and has a second thickness between the insulating layers and thesemiconductor pattern in the second direction, wherein the secondthickness is smaller than the first thickness.
 4. The three-dimensionalsemiconductor memory device of claim 2, wherein each of the first chargetrap layers is thicker than the second charge trap layer in the seconddirection.
 5. The three-dimensional semiconductor memory device of claim1, wherein each of the first charge trap layers surrounds a portion ofthe semiconductor pattern.
 6. The three-dimensional semiconductor memorydevice of claim 1, wherein the second energy band gap of the secondcharge trap layer is smaller than a third energy band gap of the tunnelinsulating layer.
 7. The three-dimensional semiconductor memory deviceof claim 1, wherein the first charge trap layers have a first conductionband energy level, the second charge trap layer has a second conductionband energy level, and the tunnel insulating layer has a thirdconduction band energy level, wherein a difference between the first andsecond conduction band energy levels is greater than a differencebetween the second and third conduction band energy levels.
 8. Thethree-dimensional semiconductor memory device of claim 1, wherein thesecond charge trap layer is disposed between the first charge traplayers and the blocking insulating layer, the second charge trap layeris disposed between the first charge trap layers and the tunnelinsulating layer, and the second charge trap layer covers top and bottomsurfaces of the first charge trap layers.
 9. The three-dimensionalsemiconductor memory device of claim 1, wherein the second charge traplayer is disposed between the gate electrodes and the semiconductorpattern, and the second charge trap layer is disposed between theinsulating layers and the semiconductor pattern.
 10. Thethree-dimensional semiconductor memory device of claim 1, wherein theblocking insulating layer and the tunnel insulating layer extend in thefirst direction, and the blocking insulating layer contacts the tunnelinsulating layer in an area between the insulating layers and thesemiconductor pattern.
 11. The three-dimensional semiconductor memorydevice of claim 1, wherein the first charge trap layers comprisepolysilicon, germanium (Ge), tungsten (W), nickel (Ni), or platinum(Pt), and the second charge trap layer comprises silicon nitride orsilicon oxynitride.
 12. A three-dimensional semiconductor memory device,comprising: an electrode structure comprising a plurality of gateelectrodes and a plurality of insulating layers, wherein the gateelectrodes and the insulating layers are alternately stacked on asubstrate, and a side surface of the electrode structure is recessed inareas corresponding to the gate electrodes to define a plurality ofrecess regions; a semiconductor pattern extending in a first directionsubstantially perpendicular to a top surface of the substrate andcrossing the side surface of the electrode structure; a plurality offirst charge trap layers respectively disposed in the recess regions ofthe electrode structure, wherein the first charge trap layers surroundthe semiconductor pattern; a tunnel insulating layer disposed betweenthe first charge trap layers and the semiconductor pattern; a blockinginsulating layer disposed between the first charge trap layers and theelectrode structure; and a second charge trap layer, wherein the secondcharge trap layer continuously extends between the blocking insulatinglayer and the first charge trap layers, and the second charge trap layercontinuously extends between the tunnel insulating layer and the firstcharge trap layers, wherein the first charge trap layers are formed of amaterial having a first energy band gap, and the second charge traplayer is formed of a material having a second energy band gap largerthan the first energy band gap.
 13. The three-dimensional semiconductormemory device of claim 12, wherein the second charge trap layer contactstop and bottom surfaces of each of the first charge trap layers.
 14. Thethree-dimensional semiconductor memory device of claim 12, wherein thesecond charge trap layer extends in the first direction, the secondcharge trap layer is disposed between the tunnel insulating layer andthe first charge trap layers, and the second charge trap layer isdisposed between the tunnel insulating layer and the blocking insulatinglayer.
 15. The three-dimensional semiconductor memory device of claim12, wherein the blocking insulating layer contacts the tunnel insulatinglayer in an area between the insulating layers and the semiconductorpattern.
 16. The three-dimensional semiconductor memory device of claim12, wherein the blocking insulating layer extends in the firstdirection, and conformally covers the recess regions of the electrodestructure.
 17. The three-dimensional semiconductor memory device ofclaim 12, wherein the second energy band gap of the second charge traplayer is smaller than a third energy band gap of the tunnel insulatinglayer.
 18. The three-dimensional semiconductor memory device of claim12, wherein the first charge trap layers have a first conduction bandenergy level, the second charge trap layer has a second conduction bandenergy level, and the tunnel insulating layer has a third conductionband energy level, wherein a difference between the first and secondconduction band energy levels is greater than a difference between thesecond and third conduction band energy levels.
 19. Thethree-dimensional semiconductor memory device of claim 12, wherein thetunnel insulating layer extends in the first direction and surrounds aside surface of the semiconductor pattern.
 20. The three-dimensionalsemiconductor memory device of claim 12, wherein a thickness of thesecond charge trap layer is smaller than a thickness of each of thefirst charge trap layers in a second direction, wherein the seconddirection is substantially parallel to the top surface of the substrate.21-34. (canceled)